Proteins are basic building blocks and workhorses of biology. A fundamental limitation of proteins is their inadequacy in covalent bonding via side chains. This application will break this natural barrier by genetically introducing new covalent bonds into proteins in live cells. The principle of the approach is to use a novel amino acid to react with natural amino acid residues in proteins. However, huge challenges are imposed by the contradictory demands on bioreactivity, genetic encoding, and specificity of bond formation. Our hypothesis and innovation is to enable the new amino acid to react with the target natural amino acid only when they are in proximity, thus permitting building the new covalent bond in proteins in live cells. New chemistries suitable for such reactions under physiological conditions will be developed. The identified chemical functionality will be installed into proteins in the format of new amino acids through protein translation in live cells. Using this new covalent bonding strategy, we will build light-sensitive nano-bridges onto proteins as a general method to optically regulate protein function for noninvasive studies in cells and in vivo. In the long run, e will further develop these new covalent bonds for studying protein networks and protein-nucleic acid interactions involved in various diseases and for generating new protein therapeutics. The success of this project will lead to a new dimension for researching and engineering proteins and biological processes by harnessing the new covalent linkages inaccessible to natural proteins, fundamentally impacting basic biological studies, biotechnology, biotherapeutics, and synthetic biology.